The present invention relates to a check valve as used for bags for containing therein goods which have to be stored under good conditions, for instance grains such as rice, and other foods or pulverulent or granular goods or materials liable to generate gases during storage in the bag, the check valve being used to discharge only fluid such as excessive air from the bag while preventing the outside air from entering into the bag. More particularly, the invention relates to an improvement of a check valve of a kind having a filter.
A check valve or fluid discharge tube of the kind having a filter is disclosed in Japanese Utility Model Application No. 12891/89 (Utility Model Application Laying Open No. 105877/90) and Japanese Utility Model Application No. 68350/89 (Utility Model Application Laying Open No. 8105/91) which were filed by the same applicant as this application. Such prior known check valve comprises a filter formed by a plastic nonwoven fabric folded over onto itself and mounted around a mouth portion formed in a base end portion of a flat fluid flow tube, and the interior of the base end portion of the flat fluid flow tube communicates with the exterior of said base end portion only through said filter.
This prior known check valve or fluid discharge tube is practically effective to discharge only gas or liquid from a bag to which the check valve or fluid discharge tube is mounted and to prevent outside air from entering into the bag. On the other hand, such check valve or fluid discharge tube has a problem that it is difficult to discharge the gas or liquid smoothly from the bag since the mouth portion of the flat fluid flow tube is extremely narrow so that the mouth portion of the fluid flow tube is sometimes closed and necessary discharge of the fluid can not always be effected.